Broadband wireless communications call for high data-rate and high performance. Temporal channel variations and time-selective fading, however, may result in lower data-rate and an overall decrease in system performance. Time-selectivity may arise for a variety of reasons, such as oscillator drifts, phase noise, multipath propagation, and relative motion between the transmitter and the receiver. Therefore, it is important for broadband wireless applications to design single- or multi-antenna systems that account for time-varying channels.